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  #1  
Old 10-25-2015, 09:15 AM
bbogue bbogue is offline
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Default 4100 base gasket

My 61 has 66-type spacer under the 4100 freshly rebuilt carburetor. This spacer has the front 2 holes partially connected and has a vacuum connection which I currently use for my vacuum advance which helps cooling by advancing timing at idle. I have Felpro 60059 4-hole gaskets above and below the spacer. I can find no vacuum leaks. I have a low rpm misfire usually noted when cold that now seems also to be present warm as well. The misfire seems to be reduced by turning in the idle mixture screws, to a point. These are currently at 1 1/4 turns. I noticed that the gasket under the carb is slightly abraided in the center, under the balance tube area, making me wonder if the gasket is interfering with whatever these tubes do. When I took the carb off the engine the carb base gasket was noted to be a homemade single hole affair, which makes me wonder if my 4-hole gasket is incorrect. I note with interest that the base gasket for the 1960 Bird with 352 engine appears to be the single hole type and wondered if perhaps my 61 was cobbled from leftover 1960 parts. FWIW, I also noticed recently when I was adjusting float levels that sometimes the front bowl level would be correct, then not. I can find no vacuum leaks but I have fixed several, beginning with a ruptured vacuum advance. The misfire began about the time the vacuum advance ruptured. I plan to replace the spacer with the correct 61 spacer and experiment with a single hole spacer under the carb. I will also replace the carb needles in case I damaged them in setting float levels. Any advice would be appreciated.
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  #2  
Old 10-25-2015, 09:35 AM
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Default 4100 base gasket

Bill, it was a pleasure welcoming you to the Forum! I am not qualified to comment on the problem you are troubleshooting, but we have many terrific techies on here who are. Once they start waking up, they should be commenting on the problem you are having. Thanks for the detailed report on what you are experiencing. That certainly helps. If you have not looked at the Advertisements Forum yet, you will find all the major Tbird parts houses listed there. If you need their free catalogs, you can call them or email them to ask for them. They will come in handy when chasing down parts and costs. We also have a pretty good Technical Resource Library (TRL) which link can always be found under my signature and that of John Pizzi ~ jopizz, and in the TRL forum. There is nothing that I can think of regarding the problem you are having in it though.
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  #3  
Old 10-25-2015, 12:02 PM
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Bill,

I'm not sure what kind of spacer you have. A '66 spacer only has a small vacuum tube coming out of the front and is very thin. A 64-65 spacer is thicker and has a coolant port in the front and rear passenger side and a vacuum port for a pcv valve in the rear center. Can you email me a picture of your setup. A Fel-Pro 60059 four hole gasket should work fine above the spacer but in order to use the vacuum port in the rear you need a Fel-Pro 13303. However, you should be using the vacuum port in the carburetor for your vacuum advance and not the spacer. If you don't have the vacuum port in the carb plugged off that's probably why you have a misfire.

John
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  #4  
Old 10-25-2015, 03:58 PM
bbogue bbogue is offline
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Quote:
Originally Posted by jopizz View Post
Bill,

I'm not sure what kind of spacer you have. A '66 spacer only has a small vacuum tube coming out of the front and is very thin. A 64-65 spacer is thicker and has a coolant port in the front and rear passenger side and a vacuum port for a pcv valve in the rear center. Can you email me a picture of your setup. A Fel-Pro 60059 four hole gasket should work fine above the spacer but in order to use the vacuum port in the rear you need a Fel-Pro 13303. However, you should be using the vacuum port in the carburetor for your vacuum advance and not the spacer. If you don't have the vacuum port in the carb plugged off that's probably why you have a misfire.

John
John, thanks for responding.
The 61 and 66 spacers are identical except for the vacuum tube which I had capped for a while until I learned from the FE engine board about how increased timing by using manifold vacuum vs ported vacuum for vacuum advance helps cooling at idle during hot weather. I tried it and it works. A little controversial but it works for me. This has no impact on my misfire as I have tried it both ways. And, I did cap the vacuum port on the carb when I changed. The 61 and 66 spacers are not heated nor is there a PCV fitting. These are much thinner than the 62-65 spacers. Phenolic vs aluminum, too. They also do not have the recessed area under the carb air balance area like the 62-65 do. There is one other difference between the 61 and 66 spacers. The 66 front 2 holes are connected for about 25% of their circumference. I really don't think my issue is the spacer but I'm going to try a 61 just to be sure. That, and a perimeter gasket vs the cloverleaf type as well. Mike of Mike's carburetors insists that the perimeter gasket is the right one. This would remove a partial obstruction in the air balance area and let the chambers "talk" better. Thanks John. I will post how my experiments go.

Bill
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  #5  
Old 10-25-2015, 04:38 PM
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Your 4100 carburetor uses manifold vacuum also so it doesn't matter whether you use the spacer or carburetor. The vacuum port on the carburetor is below the throttle plates.

John
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  #6  
Old 10-25-2015, 05:01 PM
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Default Sorry, I must disagree. Maybe I misunderstand.

Quote:
Originally Posted by jopizz View Post
Bill,

I'm not sure what kind of spacer you have. A '66 spacer only has a small vacuum tube coming out of the front and is very thin. A 64-65 spacer is thicker and has a coolant port in the front and rear passenger side and a vacuum port for a pcv valve in the rear center. Can you email me a picture of your setup. A Fel-Pro 60059 four hole gasket should work fine above the spacer but in order to use the vacuum port in the rear you need a Fel-Pro 13303. However, you should be using the vacuum port in the carburetor for your vacuum advance and not the spacer. If you don't have the vacuum port in the carb plugged off that's probably why you have a misfire.

John
Quote:
Originally Posted by jopizz View Post
Your 4100 carburetor uses manifold vacuum also so it doesn't matter whether you use the spacer or carburetor. The vacuum port on the carburetor is below the throttle plates.

John
With great respect of your knowledge and experience, what I have read and experienced differs. Maybe there was a change in the 4100 after 61. My 61 shop manual says "At low engine speeds, or at idle, spark advance is not necessary. Because the vacuum passage opening in the carburetor is above the closed throttle plate, there is no vacuum to the diaphragm."

This seems to be confirmed by the difference in timing at idle when I switch from the carb to the spacer for vacuum to the vacuum advance. Timing doesn't change when the carb is the source but advances when the spacer is the source.

Am I mistaken?

Thanks.

Bill
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  #7  
Old 10-25-2015, 05:12 PM
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If you turn your carburetor upside down and put a wire through the vacuum port you'll see it comes out below the throttle plates. Every 4100 I've worked on has it that way. If yours is different I'd like to see it. I'm not saying you're wrong. I'm just going by my own experience. Every car that I've timed that has a 4100 carburetor I've had to plug the vacuum port.

John
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  #8  
Old 10-25-2015, 05:24 PM
bbogue bbogue is offline
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Default Ok.

I will pass a wire through when I have it off next and post the results.

Thanks for trying to help.

Bill
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  #9  
Old 10-25-2015, 07:15 PM
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If you find that your carburetor has ported vacuum I would definitely like to know. That would be an oddity I'd like to make note of. Thanks.

John
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  #10  
Old 10-26-2015, 01:31 PM
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Bill,

I stand corrected. After digging out an old 4100 that I had laying around it appears that the vacuum port is indeed above the throttle plates which is odd because when I changed over to an Edelbrock and had the choice I set it to manifold vacuum because it seemed to me that there was vacuum at idle with the old carb. Maybe the throttle plates just weren't closed all the way. Regardless you are correct about using manifold vacuum. When I set my Edelbrock to ported vacuum the low speed performance seemed terrible. When I changed it to manifold vacuum the car seemed to take off much better.

As to your misfire issue what is the condition of your fuel tank. I've found most misfire problems are due to dirt in the idle passages of the carburetor. If you can make the condition better by adjusting the mixture screws it sounds like it is fuel related. On my '66 I used the standard Fel-Pro four hole gaskets above and below the spacer and it ran fine so I doubt the gaskets or spacer are the problem. Try removing the mixture screws and spray some carb cleaner in the holes. That's worked for me a few times.

John
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